1. Field of the Invention
This invention relates to a container for use in blood test. More particularly, it relates to a vacuum blood-collection tube in which a whole sample of blood is collected from the person to be tested, and which is centrifugated to obtain the serum from the sample.
2. Description of the Prior Art
The rapid advances in techniques for clinical laboratory tests, along with the wider use of blood test, including serum biochemistry tests, serum immunological tests, corpuscle tests, and so on, are contributing to the prevention of disease and also to diagnosis at early stages. The majority of blood tests are serum tests, and usually the serum that is required for such tests is collected as blood in a container for use in blood tests, and allowed to coagulate; the serum is then collected by centrifugation, by which the blood clot (a mass made of a gel mixture of fibrin and blood corpuscles) is separated.
Syringes are used to collect blood from the person to be tested, but recently, a blood-sampling method in which vacuum blood-collection tubes are used is also available. When vacuum blood-collection tubes are used to collect blood, the blood is collected into the vacuum blood-collection tube by the introduction of vacuum conditions through a special blood-collection tube holder.
The raw materials used for vacuum blood-collection tubes are either synthetic resins such as polymethylmethacrylate, etc., or glass. However, in vacuum blood-collection tubes made of these raw materials, when the blood is collected, quite a long time is required for the blood to coagulate so that the serum and the blood clot can be separated, and the serum that is required for the test can not necessarily be available rapidly. This becomes a particular problem when the test is an emergency one. Even in vacuum blood-collection tubes made of glass, in which blood coagulation time is shorter, from 40 to 60 minutes are required after the blood is collected until coagulation has taken place. When vacuum blood-collection tubes made of synthetic resins are used, it is necessary to allow the tube to stand for four hours or more, in practice. Also, in vacuum blood-collection tubes made of synthetic resins or glass, the fibrin and the blood clot in the form of a gel readily adhere to the side of the tube in solidified form, which reduces the sample volume of the serum. In addition, fibrin readily remains in the serum, and for that reason, causes a problem by interfering with serum biochemistry test results. When vacuum blood-collection tubes made of glass, which gives relatively a good separation of the serum, are used, the separation becomes extremely poor when the temperature is 15.degree. C. or below, so that the separation is poor in the low-temperature conditions of winter.
When extremely fine grains of an inorganic substance such as glass, etc., are attached to the walls of the tube, the coagulation time of the blood is shortened. When a separating agent incorporating silicon oil, powdered silicon compounds, etc., is present in the blood-collection tube, this causes an increase in the separability of the serum. Such separating agents use the property of thixotropy, and are prepared so as to have a specific gravity of the intermediate between that of the serum and the blood clot. For that reason, after the blood that has been collected is allowed to coagulate, and when the blood-collection tube is placed in a centrifugal field, the separating agent moves to the interface between the serum layer and the clotted blood layer, separating them. If it will take time until the various kinds of tests will take place on the sample serum prepared by the above-mentioned process, the blood-collection tube is stored as it is at a temperature of less than 4.degree. C. However, the possible storage time is relatively short, being about 48 hours in the case of blood-collection tubes made of glass; even in blood-collection tubes made of polymethylmethacrylate, the time is as short as about 72 hours.
If vacuum blood-collection tubes are stored having internal low pressure before blood is collected, then, because the collection tube has some permeability to gas, the low-pressure conditions inside the tube are rapidly lost, due to atmosphere oxygen, carbon dioxide, water vapor, etc.
To solve the above-mentioned problems, vacuum blood-collection tubes are ordinarily vacuum-wrapped in a separate wrapping material. The wrapping material used for the vacuum-wrapping is, for example, a metal can, or a laminated film of aluminum foil, etc. Metal cans are rigid, so they are excellent in the protection of vacuum blood-collection tubes. In addition, they act as excellent gas barriers. Their defects are that they are heavy and bulky. They are also expensive. Laminated films of aluminum foil are flexible, and have the advantages of not being hard or bulky. However, in making the vacuum blood-collection tube air-tight, there is the possibility of injuring them by crushing. The resistance and the strength against being ripped of aluminum foil are inferior, and pinholes readily form when, for instance, a section of the foil is crumpled. Once a gas such as oxygen has been allowed into the inside of the wrapping material of aluminum foil, the low-pressure conditions inside the vacuum blood-collection tube are lost. Accordingly, the ability of aluminum foil to act as a gas barrier is imperfect.